Actually even though these "services" are looking like similar, cover different fields,
An agend is just helping you to register your company and is an official POC between you and governmental institutions. They help you with filling papers, give their address for registration but for sure will not help you in case of lawsuit etc.
Attorney/lawyer is able to help you with company registration, but most probably will not agree to be your registered agent, however may advice that you can be an agent your yourself (yup, it's possible).